1. Field of the Invention
The present invention generally relates to the field of optic attenuators, and more particular to a variable optic attenuator capable of fine adjustment of the attenuation thereof.
2. The Related Arts
Optic attenuators are widely used in controlling intensity of optic signals transmitted in an optic network. Optic attenuators are classified as fixed attenuators and variable attenuators. A fixed attenuator provides a fixed attenuation to optic signals, while a variable attenuator allows adjustment of attenuation of the optic signals. A variety of variable attenuators are available among which axially separating ends of axially aligned optic fibers to form a gap therebetween is one of the most commonly used methods. The attenuation of attenuators of this kind is in general dependent upon the distance between the two optic fibers. Thus, by axially displacing one fiber relative to the other to change the distance therebetween, the attenuation that can be achieved on optic signals through the fibers can be controlled.
One form of embodying the axial displacement of the optic fiber is to make a plug type connector carrying a first fiber for mating with a socket type connector carrying a second fiber. Axial displacement is performed on the first fiber inside the plug type connector. An example is shown in U.S. Pat. No. 5,734,778 wherein a screw mechanism is attached to a ferrule carrying the first optic fiber. The screw mechanism is capable to convert turning of a nut into linear displacement of the ferrule. Such a device, however, suffers limitation in further fine tuning. The linear displacement is in general dependent upon the screw pitch. Theoretically, a finer tuning can be obtained by decrease of the screw pitch. However, physical limitation prevents the screw pitch to be decreased unlimitedly.
It is thus desirable to provide a variable optic attenuator capable of finer tuning of the attenuation thereof for overcoming the above mentioned problem.
Accordingly, an object of the present invention is to provide a variable optic attenuator capable of fine adjustment of attenuation on optic signals.
Another object of the present invention is to provide a variable optic attenuator employing a double screw mechanism for fine adjustment of attenuation.
A further object of the present invention is to provide a plug type optic attenuator capable of fine adjustment of attenuation.
To achieve the above objects, a variable optic attenuator in accordance with the present invention is embodied in the form of a plug type connector carrying a first fiber for selectively mating with a socket type connector carrying a second fiber with a distance separating the fibers for attenuating optic signals passing therethrough. The attenuator comprises a tubular body to be coupled to the socket connector with a front end. A double screw mechanism carrying the first fiber is attached to a rear end of the body with the first fiber extending through the body to axially align with the second fiber of the socket connector. The double screw mechanism includes a connecting nut attached to the rear end of the body and defining an inner-threaded bore. A tubular knob has external threading of first screw pitch and inner threading of second screw pitch different from the first pitch. The external threading of the tubular knob engages the inner threaded bore of the connecting member. An elongate rod defining a central bore for receiving and retaining the first fiber is received in the tubular knob. The rod has external threading mating the inner threading of the knob whereby rotating the knob induces different linear displacements of the knob and the rod, dependent upon the screw pitches, in opposite directions. The first fiber is thus moved a displacement corresponding to the difference of the displacements of the knob and the rod.